Moving coil voltage regulator



Feb. 11, 1936.

EJ D. T. NORRIS MOVING CQI L VOLTAGE REG UL ATOR Filed May 51, 1935 32%? r: IL

Fig 9.

Patented Feb. 11, 1936 UNITED STATES PATENT OFFICE MOVING COIL VOLTAGE REGULATOR Eric Douglas Tobias Norris, Hollinwood, England, assignor to Ferranti Electric Inc., New York.

Application May 31, 1935, Serial No. 24,437 In Great Britain April 24, 1934 6 Claims.

This invention relates to voltage regulators of the type embodying essentially a pair of fixed coils mutually associated so as to possess considerable leakage reactance, and a third coil short circuited on itself and devoid of any moving iron core, which latter coil is capable oi being moved into positions adjacent to either of said firstnamed coils or intermediate thereof.

Voltage regulators of this type possess the following desirable characteristics:--

(a) No moving iron.

(b) No flexible connections or sliding electrical contacts.

to) No sliding magnetic Joints or small air gaps.

(d) No windings in slots.

(e) No current breaking switches.

(I) Sinusoidal no-load current.

(a) Relatively low mechanical forces.

In voltage regulators hitherto employed the sum of the individual impedances of the said pair of fixed coils is substantially constant for all positions of the moving coil, thus resulting in a substantially constant no-load current irrespective of the position of the moving coil but I have found that the load impedance of the regulator and consequently the voltage drop through the regulator due to load current, depends upon the position of the moving short-circuited coil and this voltage drop is much larger when the moving coil is midway between the two fixed coils than when it is nearer either fixed coil. This is due to the fact that the said load impedance depends, among other things, on the leakage impedance of one of the fixed series-connected coils in parallel with the leakage impedance of the other fixed series-connected coil.

As a general statement if the sum of the individual impedances of two coils is constant the total impedance created by connecting the coils in parallel is not constant but has a maximum value when the individual impedances of the two coils are equal.

In voltage regulators of the type in question this occurs when the moving short-circulted coil is in the mid position between the two fixed coils. The load impedance of such regulator, and consequently the voltage drop through the regulator due to load, is not, therefore, constant but depends upon the position of the moving coil and is a maximum when the moving coil is in the midway position.

Referring to the accompanying diagrammatic drawing:

Figure l is an electrical diagram indicating the connections of the coils of a known form of voltage regulator and the connections of the coils to external circuits.

Figure 2 is a vertical cross-sectional view of a construction of voltage regulator embodying the 5 present invention.

Figure 3 is an electrical diagram indicating the electromagnetic relationship between certain of the coils of Figure 2.

Figure 4 is a vertical cross-sectional view of a 10 voltage regulator embodying the present invention but having a modified arrangement of fixed coils.

Figures 5 and 6 are electrical diagrams illustrating typical circuit arrangements to which the 15 voltage regulator of Figure 4 may be applied.

Figure 7 is a vertical cross section of a voltage regulator embodying the present invention but having a further modified arrangement of coils.

Figure 8 is a sectional plan thereof, whilst Figures 9 and 10 are electrical diagrams showing typical circuit arrangements to which the voltage regulator of Figures 7 and 8 may be applied.

Referring, for example, to the known voltage regulator illustrated in Figure 1 the two fixed coils between which there is considerable leakage reactance are indicated at 2 and 3 and a moving short-circuited coil adapted to be moved into the proximity of coils 2 and 3 alternatively is indl- 30 cated at 4 and a further fixed coil closely associated with coil 2 is indicated at I. The windings 2, 3 are connected across the primary circuit P1 and P: so that the primary voltage is divided between these windings in accordance with their 35 respective impedances. The secondary circuit S1. S2 comprises the three coils I, 2 and 3. The fixed coils may be arranged either in sandwich form or in mutually encircling fashion and in either case the leakage impedance between the fixed coils 2 40 and 3 is substantially equal to the sum of the leakage impedances between the fixed coil 2 and the moving coil 4 and between the fixed coil 3 and moving coil 4 and this sum is substantially constant for all positions of the moving coil. 45 With these relations the impedance to load current of the regulator is substantially greater with the coil in the mid position as explained above.

Means have been proposed for reducing this impedance in the mid position by means of auxso iliary coils and the present invention has for its object to provide simplified means of reducing this mid position load impedance without necessitating the use of any auxiliary coils.

The invention consists in an A. C. voltage 6;

regulator of the type indicated comprising two fixed coaxial coils connected in series opposition and displaced with respect to one another in an axial direction, together with a movable shortcircuited coil encircling or encircled by the fixed coils when viewed axially, both of said fixed coils being so arranged that when the moving coil is midway between the fixed coils the sum of the leakage impedance between the individual fixed coils and the movable coil is less than the leakage impedance between the fixed coils.

The invention also consists in an A. C. voltage regulator as set forth above wherein the distance between adjacent ends of the two fixed coils measured in an axial direction is less than the axial length of the movable short-circuited coil.

The invention also consists in an A. C. voltage regulator as set forth above including also a further fixed coil closely associated electromagneticaily with one of said fixed coils.

The invention also consists in an A. C. voltage regulator as set forth above including also a pair of further fixed coils closely associated electromagnetically with said fixed coils respectively.

The invention also consists in an A. C. voltage regulator substantially as hereinafter described with reference to Figure 2, Figure 4 or Figures 7 and 8 of the accompanying drawing.

In carrying the invention into effect according to one example illustrated in Figure 2 as applied to a voltage regulator of the general form indicated in Figure l, I provide on the centre limb a of a three-limbed laminated iron core two fixed coils 2, 3 possessing considerable leakage reactance, these coils being disposed on the limb with mutual axial separation.

A third fixed coil encircling the coil 2 is provided and all three coils are connected electrically in series as indicated in Figure 2; the coils 2 and 3, however, are connected in opposition as indicated in Figure 3. The limb a and fixed coils are encircled by a short-'circuited coil 4 which is devoid of any moving iron core and is adapted to be moved into any desired position along the limb a.

The short-circuited coil 4 is of sufilcient axial length to overlap the fixed coils when the moving coil occupies its mid position on the centre limb.

When the movable coil 4 occupies its mid position the sum of the leakage impedances between the two fixed coils 2, 3 and the movable coil 4 is less than the leakage impedance between the said two fixed coils themselves and under these conditions the impedance to the load current with the movable coil in its mid position is very greatly reduced and in consequence with the movable coil in this position the voltage drop through the regulator due to the load is reduced.

In carrying the invention into effect according to a further example as illustrated in Figure 4, I provide only two coils 2, 3 on the centre limb a of a three-limbed laminated iron core, these coils being connected electrically in series opposition (Figure 3), being encircled by a concentric shortcircuited moving coil 4 and being separated axially as before.

One typical application of the voltage regulatorindicated in Figure 4 is shown in Figure 5 in which the fixed coils 2, 3 are connected across the primary leads P1, P2. the secondary circuit of which S1, S2 includes windings 5, 6 in series, the latter being Joined in parallel with the coil 2. This arrangement enables the voltage across the secondary leads S1, S2 to be boosted to a varying degree above the voltage across the primary leads P1, P2 as the coil 4 is moved from the full line position to the dotted line position.

In the arrangement illustrated in Figure 6, the voltage regulator is shown as applied to a method for transformer tap changing under load, the regulator being adapted to be connected to various selected tapping points at will.

In operation, with this arrangement, the regulator being connected as shown in Figure 6, if it be desired to open the switch I) the short-circuited winding 4 is moved so as to be in close electromagnetic association with the upper fixed coil 3 so that this coil will have a low impedance compared with that of the fixed coil 3.

In these circumstances, since the current in the two fixed coils will be practically inversely proportional to their respective impedances, the bulk of the current will be carried by the coil 2. The current in the coil 3 being very small, the circuit through this coil may now be discontinued by opening the switch b. The lower end of the coil 3 may now be connected to another tapping point on the transformer winding c and the movable coil 4 moved into close electromagnetic relationship with the coil 3 to divert the bulk of the current through coil 3 whereupon the switch at d may be opened.

Under running conditions the short-circuited winding 4 can be left in close electromagnetic relationship with one or other of the choke coils 2, 3 or in an intermediate position as may be desired.

In carrying the invention into effect according to a further example illustrated in Figures 7 and 8, in addition to two axially separated fixed coils 2 and 3 connected in series opposition further fixed coils I and l are provided respectively encircling and closely electromagnetically coupled to the coils 2 and 3, an encircling concentric shortcircuited movable coil 4 being provided as before.

One typical application of the voltage regulator of Figures 7 and 8 as a main transformer is shown in Figure 9, the axially separated windings 2 and 3 connected in series opposition being connected across the primary leads Pl, P2 and the windings I and 1 being connected in the secondary mains S1, S2, these windings, however, being connected in the same sense.

With this arrangement when the coil 4 is moved into close proximity to the windings l and 2, the voltage across winding 2 will be small and that across 3 large, whereas with the winding 4 in close proximity with the windings 3 and l opposite conditions will obtain. By this means either a positive or a negative voltage boost may be given to the secondary circuit S1. S2.

A further typical application of the voltage regulator of Figures '7 and 8 is illustrated in Figure 10 in which the windings 2, 3 and I, I are connected across mains Pl, P2. The windings 2 and I are axially separated from the windings 3 and l and the windings 2 and 3 and l and l. are connected in series opposition.

The leads S1, S2 are connected to a booster transformer, the secondary S3, S4 of which is in series with the line P1.

The ratio of this booster transformer is suitably chosen to give the desired buck and boost in the load circuit and assuming coils l, 3 and 2, l have the same number of turns, then with the shortcircuited coil 4 at one end of the limb a. a maximum voltage is introduced in the secondary winding of the series transformer, thus boosting the voltage Pl, P2.

As the short-circuited coil 4 moves to the other end of the limb this series voltage falls to zero 1 iii" and increases in a negative direction until it is of the same magnitude as before but now bucking the supply voltage P1, P1.

In practice I have found that the load impedance of voltage regulators embodying the present invention may easily be reduced to one-third or one-quarter of the figure usually entailed.

I claim as my invention:

1. An A. C. voltage regulator of the type indicated comprising two fixed coaxial coils connected in series opposition and displaced with respect to each other in an axial direction, together with a movable short-circuited coil, the fixed coils and said movable coil mutually encircling when viewed axially, said fixed coils being disposed to possess mutual leakage impedance which is greater than the sum of the leakage impedance between the individual fixed coils and the movable coil when the moving coil is midway between the fixed coils.

2. An A. C. voltage regulator as claimed in claim 1 wherein the distance between adjacent ends of the two fixed coils measured in an axial direction is less than the axial length of the movable shortcircuited coil.

3. An A. C. voltage regulator as claimed in claim 1 including also a further fixed coil closely associsearch noun.

ated electromagnetically with one of said fixed coils.

4. An A. C. voltage regulator as claimed in claim 1 including also a pair of further fixed coils closely associated electromagnetically with said fixed coils respectively.

5. An A. C. voltage regulator as claimed in claim 1 for boosting or bucking voltage wherein two electrically separate windings connected in the same sense are magnetically associated respectively with said individual fixed coils.

6. An alternating current voltage regulator having windings consisting of two fixed coaxial coils in series opposition and a short-circuited coil capable of movement in relation to said fixed coaxial coils, said movable and fixed coils mutually encircling when viewed axially said shortcircuited coil constituting the sole movable electromagnetic element and said fixed coils being disposed to possess mutual leakage impedance which is greater than the sum of the leakage impedance between the individual fixed coils and the movable coil when the latter coil is midway between the said fixed coils.

ERIC DOUGLAS TOBIAS NORRIS. 

